Around 5 p.m. on Tuesday a construction site at Fourth Street and China Basin in Mission Bay caught fire. Emergency in SF reports the fire was burning on the ninth floor of the construction site:

Update, 5:40 p.m.: SFFD has now called a fourth alarm. There are reportedly some 125 firefighters and 35 trucks on the scene. The fire may also be spreading to a second building and neighbors are being evacuated.

CBS5/KPIX has live video from the air. The news choppers appear to have gone home for the night, so we've replaced the stream with a time-lapse video sent shot from an office building across town and sent in by reader Jake D.:

Update, 5:50 p.m.: According to retired San Jose Fire Captain Vincent Sciortino, speaking with KPIX5, the fire is particularly bad because the building is under construction without any suppression or sprinkler systems. The heat could be enough to start shattering windows and peeling paint off of buildings nearby. KPIX is also reporting a 5th alarm has been called.

According to Captain Sciortino, the building is essentially "a pile of fuel" and firefighters are working to contain the fire, but it seems likely that the partially finished construction will burn completely to the ground before it is under control. San Francisco Fire Department spokesperson Mindy Talmadge says the goal is not to save the building, but to keep the fire from spreading to adjacent buildings. The building was reportedly a residential development with 360 apartment. No injuries have been reported so far.

Update, 6 p.m.: We're getting reports from NBC Bay Area that a sixth alarm has been called. (Scratch that: LA Times and NBC Bay Area were reporting, but we don't have any official sources on a 6th alarm. -Ed.) The top two or three floors of the building are completely engulfed in flames and parts have begun to collapse.

Update, 6:15 p.m.: The fire has spread to an adjacent building along Fourth Street, which is reportedly a UCSF property.

According to a representative from the construction company who was in the site earlier Tuesday afternoon, the building is part of the Mission Bay 360 development. SF Business Times reports the project, which will most likely be completely lost, was valued around $115 million when completed. The building that caught fire Tuesday evening contained only 172 units of the total 360 for the project. When construction began in 2013, the developer BRE valued the apartments at an average of $630,000 per unit.

Update, 6:50 p.m. The embers seen smoldering on the adjacent UCSF-owned building have been extinguished. Most of Mission Bay 360 building that caught fire, however, has collapsed and firefighters are still working to contain. No injuries have been reported. Traffic along the Bay Bridge is also completely gridlocked.